As is known, at the present time there are two types of needles for knitting on circular knitting machines and these are known as spring beard and latch needles, respectively. The first-mentioned needles are fitted on circular knitting machines having a single needle bed or needle-holding means and, for their knitting action, the needles must be assisted by pressers which act on the hooks of the needles in order to close them and be able to cast off the loop from the previous picking-up operation across the thread retained in the hook closed by the pressure of the presser. Latch needles have attachments, called latches, which close the hooks of the needles as a result of the pressure exerted by the loop from the picking-up operation prior to a given stitch forming operation and located below the latch, in order to cast this loop off across the thread retained in the hook of the needle and it is this thread which will open the latch in the direction opposite to the previous direction, so that the said thread or already formed loop may pass behind the latch, the latter having to remain open until the thread is picked up again, this being the most common method for forming knitted fabric in flat and circular machines having one or two needle beds.
This method of knitting with needles having a radially articulated latch has certain disadvantages in flat and circular knitting machines, such as the need for great precision of adjustment of the yarn guides associated with the needles, these guides being required to cover perfectly over their width the path described by the needles during their knitting process and to protect the latches, leaving a free space for them to open and close. Maladjustment of the yarn guides may cause the latches to strike against the edges of the yarn guides as they open and break, or else close before the yarn or thread is picked up. For higher machine working speeds, there is risk of rebounding and rubbing of the latches against the yarn guides, and damage of the latches, which leads to defects in the knitted fabrics produced.
Another disadvantage when the machine has greater working speeds is that the radially articulated latches of the needles close with much more force, striking sharply against the hook of the needle and causing it or the tongue itself to break, especially when the operation is performed with very fine needles in machines of fine gauge or with many needles per inch.
Apart from these mentioned disadvantages of mechanical type, others arise due to the operation itself of knitting machines knitting with needles having a radially articulated latch, such as the release of loops, or dropped stitches, due to the fact that when a loop is cast off in a stitch forming operation, it passes across the latch, closing it abruptly and causing it to rebound, which leaves it open, the loop being simply picked up by the hook of the needle. If the loop is very long, it is loose within the hook of the needle and if the tension of the fabric produced by the machine is low, the loop may disengage itself from the hook of the needles, causing a fault known as "dropped stitches" in the fabric.
In the method hereinbefore mentioned for knitting in flat and circular knitting machines, the thread or formed loop in the hook of the needle with a radially articulated latch which produces the mechanical force for opening and closing the articulated latch of the needle has proved to be a drawback. The thread is subjected to a constant stress, since while the thread is picked up by the head or hook of the needle, the previous loop formed behind the latch compels it, by forcing it, to close over the picked-up thread, and this, as it rubs against the tongue, gives rise to separation of the fibers and, at the same time, the danger of the thread being cut, due to the fact that as the latch closes, pressed by the loop, it exerts a scissors action, consequently producing a fault in knitted fabrics of synthetic and continuous yarns which is of the kind called "fiber separation" or "nap" giving rise to fabric with cut loops.
In the case of the beard needle without a latch and assisted by a presser, apart from the fact that it cannot be operated in machines having two needle beds, there is also the disadvantage that due to the action of the presser, the hook of the needle is subjected to a constant bending stress and can break through fatigue.